The present invention relates to a curable silicone rubber composition and a product of curing thereof, particularly to an addition-type silicone rubber composition which can give a low-modulus silicone rubber by curing and a product of curing thereof.
A method for producing an elastomer by the addition reaction of an organopolysiloxane containing at least two alkenyl groups such as vinyl groups bonded to the silicon atoms with an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to the silicon atoms in the presence of a platinum catalyst is well known, and so is a process wherein an inorganic filler is added to improve the flame retardance, mechanical strengths or chemical resistance of the elastomer.
Further, it is known that the modulus of a cured silicone rubber can be lowered by adding a nonfunctional oil, such as nonfunctional silicone oil.
Although the cured rubber exhibits a lowered hardness and modulus, a silicone rubber composition containing a nonfunctional oil has several disadvantages. The oil tends to bleed on the surface of the product of curing of the composition, and thus it contaminates the material in contact therewith or causes deformation due to shrinkage. It is also noticed that the adhesion of the composition is hindered during its curing stage. These disadvantages occur even when an addition-type silicone gel not containing any filler is used instead of the above silicone rubber.
Meanwhile, there is known another method for lowering the modulus of a cured silicone rubber by reducing the amount of the inorgnaic filler to be added thereto. However, by this method the strengths of the cured rubber are so lowered that the use application of the cured rubber is limited to a special field such as potting.